En Route to Mars, The Moon

March 18, 2005: NASA has a new Vision for Space Exploration:
in the decades ahead, humans will land on Mars and explore the red
planet. Brief visits will lead to longer stays and, maybe one day,
to colonies.

First,
though, we're returning to the Moon.

Why the Moon before Mars?

"The Moon is a natural first step," explains Philip Metzger,
a physicist at NASA Kennedy Space Center. "It's nearby. We can
practice living, working and doing science there before taking longer
and riskier trips to Mars."

Right:
The Moon, an alien world in Earth's backyard. Photo credit: International
Space Station astronaut Leroy Chiao. [More]

The Moon and Mars have a lot in common. The Moon has only one-sixth
Earth's gravity; Mars has one-third. The Moon has no atmosphere; the
Martian atmosphere is highly rarefied. The Moon can get very cold,
as low as -240o C in shadows; Mars varies between -20o
and -100o C.

Even more important, both planets are covered with silt-fine dust,
called "regolith." The Moon's regolith was created by the
ceaseless bombardment of micrometeorites, cosmic rays and particles
of solar wind breaking down rocks for billions of years. Martian regolith
resulted from the impacts of more massive meteorites and even asteroids,
plus ages of daily erosion from water and wind. There are places on
both worlds where the regolith is 10+ meters deep.

Operating mechanical equipment in the presence of so much dust is
a formidable challenge. Just last month, Metzger co-chaired a meeting
on the topic: "Granular Materials in Lunar and Martian Exploration,"
held at the Kennedy Space Center. Participants grappled with issues
ranging from basic transportation ("What kind of tires does a
Mars buggy need?") to mining ("How deep can you dig before
the hole collapses?") to dust storms--both natural and artificial
("How much dust will a landing rocket kick up?").

Answering these questions on Earth isn't easy. Moondust and Mars
dust is so ... alien.

Try this: Run your finger across the screen of your computer. You'll
get a little residue of dust clinging to your fingertip. It's soft
and fuzzy--that's Earth dust.

Lunar dust is different: "It's almost like fragments of glass
or coral--odd shapes that are very sharp and interlocking," says
Metzger. (View an image
of lunar dust.)

"Even after short moon walks, Apollo 17 astronauts found dust
particles had jammed the shoulder joints of their spacesuits,"
says Masami Nakagawa, associate professor in the mining engineering
department of the Colorado School of Mines. "Moondust penetrated
into seals, causing the spacesuits to leak some air pressure."

Above:
Dust flies from the tires of a moon buggy, driven by Apollo 17 astronaut
Gene Cernan. These "rooster-tails" of dust caused problems,
which the astronauts solved using duct tape. [More]

In sunlit areas, adds Nakagawa, fine dust levitated above the Apollo
astronauts' knees and even above their heads, because individual particles
were electrostatically charged by the Sun's ultraviolet light. Such
dust particles, when tracked into the astronauts' habitat where they
would become airborne, irritated their eyes and lungs. "It's
a potentially serious problem."

Dust is also ubiquitous on Mars, although Mars dust is probably
not as sharp as moondust. Weathering smooths the edges. Nevertheless,
Martian duststorms whip these particles 50 m/s (100+ mph), scouring
and wearing every exposed surface. As the rovers Spirit and Opportunity
have revealed, Mars dust (like moondust) is probably electrically
charged. It clings to solar panels, blocks sunlight and reduces the
amount of power that can be generated for a surface mission.

For these reasons, NASA is funding Nakagawa's Project Dust, a four-year
study dedicated to finding ways of mitigating the effects of dust
on robotic and human exploration, ranging from designs of air filters
to thin-film coatings that repel dust from spacesuits and machinery.

The
Moon is also a good testing ground for what mission planners call
"in-situ resource utilization" (ISRU)--a.k.a. "living
off the land." Astronauts on Mars are going to want to mine certain
raw materials locally: oxygen for breathing, water for drinking and
rocket fuel (essentially hydrogen and oxygen) for the journey home.
"We can try this on the Moon first," says Metzger.

Right:
An Apollo 17 astronaut digs a trench to study the mechanical behavior
of moondust. [More]

Both the Moon and Mars are thought to harbor water frozen in the
ground. The evidence for this is indirect. NASA and ESA spacecraft
have detected hydrogen--presumably the H in H2O--in Martian
soil. Putative icy deposits range from the Martian poles almost to
the equator. Lunar ice, on the other hand, is localized near the Moon's
north and south poles deep inside craters where the Sun never shines,
according to similar data from Lunar Prospector and Clementine, two
spacecraft that mapped the Moon in the mid-1990s.

If this ice could be excavated, thawed out and broken apart into
hydrogen and oxygen ... Voila! Instant supplies. NASA's Lunar Reconnaissance
Orbiter, due to launch in 2008, will use modern sensors to search
for deposits and pinpoint possible mining sites.

"The lunar poles are a cold place, so we've been working with
people who specialize in cold places to figure out how to land on
the soils and dig into the permafrost to excavate water," Metzger
says. Prime among NASA's partners are investigators from the Army
Corps of Engineers' Cold Regions Research and Engineering Laboratory
(CRREL). Key challenges include ways of landing rockets or building
habitats on ice-rich soils without having their heat melt the ground
so it collapses under their weight.

Testing all this technology on the Moon, which is only 2 or 3 days
away from Earth, is going to be much easier than testing it on Mars,
six months away.